7.2. The serial port (UART)
Microcontrollers MCS-51 family have the hardware required to perform full duplex serial communication (transmit and receive simultaneously), by incorporating a UART or Universal Asynchronous Receiver and Transmitter (Universal Asynchronous Receiver-Transmitter).
The register SCON (98H, 152)
Record serial port settings .
| MSB | | | | | | | LSB |
| SM0 | SM1 | SM2 | REN | TB8 | Rb8 | IT | RI |
| 9FH | 9EH | 9Dh | 9CH | 9bh | 9AH | 99h | 98H |
SM0 - SM1. Selecting the operating mode of the serial port.
| Mode | SM0 | SM1 | Description | Operating Speed |
| 0 | 0 | 0 | Shift Register | set (clock / 12) |
| 1 | 0 | 1 | 8-bit UART | variable |
| 2 | 1 | 0 | 9-bit UART | set (clock / clock 64 or / 32) |
| 3 | 1 | 1 | 9-bit UART | variable |
SM2. Special configuration of the operating modes.
- Mode 0: SM2 has to remain at 0.
- Mode 1: If SM2 is 1, RI is not activated unless it receives the Stop bit.
- In modes 2 and 3: If SM2 is 1, enables multi-mode, and RI is not activated when the 9 th bit (Rb8) is 0.
REN. Reception control
0 -> Disable the reception.
1 -> Enable receiving characters.
Mode 0: 0 -> Air, 1 -> Front.
TB8. For communication with parity control, transmission.
Corresponding to 9 th bit (parity bit) to transmit communications of 9 bits with parity control in modes 2 and 3.
Rb8. For communication with parity check, receipt.
- Mode 0: Not used.
- Mode 1: Pick up the bit is Stop.
- In modes 2 and 3: Get the 9th bit (parity bit).
IT. Indicator or transmission interrupt flag.
This flag indicates the end of the transmission of a character. Is activated at the start of the Stop bit.
0 mode is activated at the end of 8 th bit.
It should be clear by program.
RI. Indicator or receive interrupt flag.
This flag indicates the reception of a new character is available in SBUF. Is activated at the end of 8 th bit in Mode 0, and within the Stop bit in the other modes (with the exception of multiprocessor).
It should be clear by program.
